The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As a result of environmental and other concerns, plastic containers such as polyethylene terephthalate (PET) containers are being used to package numerous commodities previously supplied in glass containers. PET containers are lightweight, inexpensive, recyclable and manufacturable in large quantities. PET containers, however, may be susceptible to distortion since they are continually being re-designed in an effort to reduce the amount of plastic required to make the container. While this strategy realizes a savings with respect to material costs, the reduction in the amount of plastic may decrease container rigidity and structural integrity.
Container rigidity and structural integrity is particularly important when these containers are filled using a hot-fill process. A hot-fill process is when a liquid product at an elevated temperature, typically between 155° F.-205° F. (68° C.-96° C.) and usually at approximately 185° F. (85° C.), is inserted into the container. When packaged in this manner, the hot temperature of the liquid commodity sterilizes the container at the time of filling.
After being hot-filled, the containers are capped and allowed to reside at generally the filling temperature for approximately five minutes at which point the container, along with the product, is then actively cooled prior to transferring to labeling, packaging, and shipping operations. The cooling reduces the volume of the liquid in the container. This product shrinkage phenomenon results in the creation of a vacuum within the container. If not controlled or otherwise accommodated, these vacuum pressures result in deformation of the container, which leads to either an aesthetically unacceptable container or one that is unstable. Hot-fillable plastic containers, therefore, should provide sufficient flexure to compensate for the changes of pressure and temperature, while maintaining structural integrity and aesthetic appearance. Typically, the industry accommodates vacuum related pressures with sidewall structures or vacuum panels. Such vacuum panels generally distort inwardly under vacuum pressures in a controlled manner to eliminate undesirable deformation.
Thus, there is a need for an improved lightweight container which can accommodate the vacuum pressures which result from hot filling, prevent container sidewall sag, while still providing a more rigid and structurally sound container that can withstand the rigors of packaging, shipping, and being handled by a consumer.